A:Answer F800 has an internal capacitor sufficient for the dashcam to close the files that it is writing. If you order their hardwire kit, it requires +batt that is always on, then +Acc that goes on with the key, and ground.
With both power lines, the camera can then transition between driving recording or parking recording modes.
Also, you do not need 2 F800. You can order the F800 or F800Pro with the rear camera and cable accessory and the one device will record both front and rear. Note the F800 pro allows larger flash cards as well as some cloud and parking features.